Photoresistor Transistor Circuit

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The transistor may directly control power to an led or bulb or may drive a relay.

Photoresistor transistor circuit. I change the sensibility of this transistor based switch circuit using 2n3904 npn bipolar junction transistor bjt and photo resistor. It stays lit as long as the photoresistor is exposed to light. On the bottom l r.

This led is red blindingly bright at 60 candela in a 10 mm package. It is a simple and powerful concept which uses transistor bc 547 npn as a switch to switch on and off the led light automatically. This is the photoresistor circuit when the photoresistor is exposed to light.

Cathode negative of led is connected with c collectr of bc 547 transistor. A light dependent resistor ldr provides a switching signal to a transistor to control a load. Like more conventional transistors the phototransistor can be used in common emitter and common collector circuits.

The photoresistor detects light levels and its resistance changes based on the amount of light it picks up. In this circuit the centre voltage divider is creating a voltage between 5 to almost 0 where the amount of light shown on the photoresistor determines this. It casts a visible beam visible for about twenty feet in a well lit room.

Base b is connected junction point of the 50k resistor ldr. Transistor as a switch using ldr. Simple transistor circuits with ldr are very common and used in many applications such as a night light and emergency lighting.

Emitter e of transistor is connected with the negative of battery. The photoresistor is rated at 80mw and series vt is 900 whatever that is. Common base circuits are not normally used because the base connection is often left floating internally and may not be available.

When exposed to light the photoresistor has very little resistance so current can flow through the circuit. The led an ltr 4206e phototransistor a 2n3904 transistor and a 1 k resistor. The led receives current and lights up.

The photoresistor is in series with 100k ohm resistor across 12vdc and off the center if this is a resistor 47k ohm driving the first of three transistors. As soon as ambient light is sensed by the circuit the motor will automatically turn on and remain on as long as the light remains. In this video we learn how to build an automatic night led light using a npn transistor and a photoresistor.

This voltage changes the amount of current going through the transistors which switches them on or off. We build a simple circuit and by it learn how transistors work. The component that allows for the light sensing in this circuit is a photoresistor.

The phototransistor can be used in a variety of different circuit configurations. A cr2032 lithium coin cell 3 v. We got the leds and batteries on ebay and the other parts are from digi key but mouser has them as well.

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